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CHMOD

Section: User Commands (1)
Updated: March 2003
Index

NAME

chmod - change file access permissions

SYNOPSIS

chmod[OPTION]... MODE[,MODE]... FILE...
chmod[OPTION]... OCTAL-MODE FILE...
chmod[OPTION]... --reference=RFILE FILE...

DESCRIPTION

This manual pagedocuments the GNU version ofchmod.chmodchanges the permissions of each given file according tomode,which can be either a symbolic representation of changes to make, oran octal number representing the bit pattern for the new permissions.

The format of a symbolic mode is`[ugoa...][[+-=][rwxXstugo...]...][,...]'. Multiple symbolicoperations can be given, separated by commas.

A combination of the letters `ugoa' controls which users' access tothe file will be changed: the user who owns it (u), other users in thefile's group (g), other users not in the file's group (o), or allusers (a). If none of these are given, the effect is as if `a' weregiven, but bits that are set in the umask are not affected.

The operator `+' causes the permissions selected to be added to theexisting permissions of each file; `-' causes them to be removed; and`=' causes them to be the only permissions that the file has.

The letters `rwxXstugo' select the new permissions for the affectedusers: read (r), write (w), execute (or access for directories) (x),execute only if the file is a directory or already has executepermission for some user (X), set user or group ID on execution (s),sticky (t), the permissions granted to the user who owns the file (u),the permissions granted to other users who are members of the file's group (g),and the permissions granted to users that are in neither of the two precedingcategories (o).

A numeric mode is from one to four octal digits (0-7), derived byadding up the bits with values 4, 2, and 1. Any omitted digits areassumed to be leading zeros. The first digit selects the set user ID(4) and set group ID (2) and sticky (1) attributes. The second digitselects permissions for the user who owns the file: read (4), write (2),and execute (1); the third selects permissions for other users in thefile's group, with the same values; and the fourth for other users notin the file's group, with the same values.

chmodnever changes the permissions of symbolic links; thechmodsystem call cannot change their permissions. This is not a problemsince the permissions of symbolic links are never used.However, for each symbolic link listed on the command line,chmodchanges the permissions of the pointed-to file.In contrast,chmodignores symbolic links encountered during recursive directorytraversals.

STICKY FILES

On older Unix systems, the sticky bit caused executable files to behoarded in swap space. This feature is not useful on modern VMsystems, and the Linux kernel ignores the sticky bit on files. Otherkernels may use the sticky bit on files for system-defined purposes.On some systems, only the superuser can set the sticky bit on files.

STICKY DIRECTORIES

When the sticky bit is set on a directory, files in that directory maybe unlinked or renamed only by root or their owner. Without thesticky bit, anyone able to write to the directory can delete or renamefiles. The sticky bit is commonly found on directories, such as /tmp,that are world-writable.

OPTIONS

Change the mode of each FILE to MODE.

-c, --changes: like verbose but report only when a change is made
-f, --silent, --quiet: suppress most error messages
-v, --verbose: output a diagnostic for every file processed
--reference=RFILE: use RFILE's mode instead of MODE values
-R, --recursive: change files and directories recursively
--help: display this help and exit
--version: output version information and exit

Each MODE is one or more of the letters ugoa, one of the symbols +-= andone or more of the letters rwxXstugo.

AUTHOR

Written by David MacKenzie.

REPORTING BUGS

Report bugs to <bug-coreutilsAATTgnu.org>.

COPYRIGHT

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